This application claims priority under 35 USC xc2xa7120 to Japanese Patent Application No. 10-325895, filed in the Japanese Patent Office on Oct. 29, 1998, and the entire contents of which are hereby incorporated by reference.
1. Field of the Invention
The present invention relates to a constant linear velocity (CLV) optical disc, and in particular, a format of the above-mentioned CLV optical disc.
2. Discussion of the Background
In order to raise the speed of accessing information recorded on an optical disc, it is necessary to control the speed of moving the optical head precisely and with high speed. When an optical disc apparatus receives from a higher-level apparatus a command to access the information, the optical disc apparatus calculates the relationship between the logical number of the information and the physical position as shown by the track number or the sector number on the optical disc, and the apparatus moves the optical head to the above-mentioned physical position.
Presently, recording on optical discs is performed according to a CAV (Constant Angular Velocity) type recording method in which the angular velocity is constant or a CLV (Constant Linear Velocity) type recording method in which the linear velocity is constant.
In the CAV method, since the amount of the information on one track is always constant regardless of recording on inner or outer circumferences of the disc, the conversion between the logical information number and the track number (numerical value) can easily be calculated, in a very short time. However, according to the CAV method, there arises a problem that the line density of the information at the outer circumference of the disc is lowered and thereby the overall memory capacity is lowered. In order to avoid lowered memory capacity, a modified CAV method has been devised wherein that the frequency of the recording signal is raised at the outer circumferential portion of the disc for the purpose of making uniform the line density on the respective inner and outer circumferential portions. However, in the modified CAV method, there arises another problem that the structure of a formatter circuit becomes complicated.
From the viewpoint of memory capacity and simplification of the formatter circuit, the CLV method is preferable over the CAV method. However, in the CLV method, the amount of the information on one track differs in accordance with the radius position on the disc, and calculating the conversion between the information number and the physical position may become further complicated. As the result, the conversion calculation cannot be done in a short time, and as a result, the access time may be increased.
In the recent years, as large-capacity optical disc media, DVD-ROM, DVD-R, and DVD-RAM, etc. have become noteworthy. Further increase s in memory capacity is continuously desired even now. Namely, it can be expected that pitch is to be narrowed more and more and thereby the size of a bit is further decreased. In such a situation, high-speed access to such a large-capacity media has become important.
Japanese Laid-Open Patent Publication No. 9-16980 entitled, xe2x80x9cA METHOD OF ACCESSING INFORMATION ON AN CLV OPTICAL DISCxe2x80x9d describes a method including the steps of: firstly determining only the moving direction of the optical head; driving, in advance, the optical head moving medium; obtaining, thereafter, the present position (track number) corresponding to the present address and the target position (track number) corresponding to the access target address by the calculation; calculating the number of tracks between the present position and the target position; and finally performing the access control.
However, there is a limitation in the realization of high-speed operation obtained in such way as mentioned heretofore. Therefore, the sufficient high-speed access cannot always be realized.
On the other hand, Japanese Laid-upon Patent Publication No. 8-279129 entitled, xe2x80x9cA METHOD OF MANUFACTURING A CLV DISCxe2x80x9d although not directed to a method of controlling the CLV, instead describes a method of arranging the sector without causing any angular positional error obtained at the time of ideally driving the CL+V. The disclosed method includes the steps of: causing the formatter to receive the start position of the start sector""s address from a cutting machine with the same angular information; previously estimating the address situated at the same neighboring angular position as that of the start address; changing the buffer length when the sector arrives at the above-mentioned estimated address; confirming thereby the arrival of the electric signal of the angular information sent from the cutting machine; sending the address signal of the next sector and thereby absorbing the variation of the angular position due to the error of the cutting start radius position and due to the change of the track pitch; and making uniform the sector angle between the different stampers.
However, according to the method as mentioned above, it is inevitably necessary to perform special processings such as the estimation of the sector arriving at the same neighboring angular position as that of the start sector and the compensation of the buffer length, etc.
As mentioned above, the conventional CLV optical disc requires much time for calculating the conversion between the logical information number and the physical position. Therefore, the speed of accessing the disc information is inevitably lowered.
Accordingly, an object of the present invention is to provide an improved CLV optical disc and the CLV type method of disc-formatting whereby calculation of the conversion between the logical information number and the physical position does not require much time and the speed of accessing the disc information is increased.
In consideration of the above, therefore, a further object of the present invention is to realize the CLV optical disc capable of facilitating the calculation of the conversion between the information number and the track number, eliminating the unevenness of the format of the disc manufactured by use of the different optical disc master 7 board (plate), and accessing the disc information with high speed.